1. Field of the Invention
The present invention relates to golf balls. More particularly, the present invention relates to improvements of dimples of golf balls.
2. Description of the Related Art
Golf balls have numerous dimples on the surface thereof. The dimples disrupt the air flow around the golf ball during flight to cause turbulent flow separation. By causing the turbulent flow separation, separating points of the air from the golf ball shift backwards leading to the reduction of drag. The turbulent flow separation promotes the differentia between the separating point on the upper side and the separating point on the lower side of the golf ball, which results from the backspin, thereby enhancing the lift force that acts upon the golf ball. Such a role of the dimples is referred to as a “dimple effect”. Excellent dimples disturb the air flow more efficiently.
Polygonal dimples disturb the air flow more efficiently. According to golf balls having polygonal dimples, a great flight distance can be attained. U.S. Pat. No. 5,338,039 discloses a golf ball having dimples with a polygonal plane shape, and with a cross-sectional shape showing a double slope. JP-A-2003-290392 discloses a golf ball having polygonal first dimples and second dimples formed on the bottom face of the first dimple. United States Patent Publication No. 2004/0152541 discloses a golf ball having polygonal dimples arranged thereon using a quasi-regular polyhedron.
Polygonal dimples are inferior in geometrical symmetry compared to circular dimples, therefore, golf balls having the polygonal dimple will be disadvantageous in terms of insufficient aerodynamic symmetry. According to the golf balls that are inferior in aerodynamic symmetry, trajectory may vary depending on the impact point. Golf players can not select the impact point of a golf ball apart from tee shots. Golf balls that are inferior in aerodynamic symmetry yield variation in the flight distance.
An object of the present invention is to provide a golf ball that can attain a great flight distance and is excellent in aerodynamic symmetry.